build: bump urllib3 from 1.25.7 to 1.25.8 in /requirements (#284)

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.25.7 to 1.25.8.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/main/CHANGES.rst)
- [Commits](urllib3/urllib3@1.25.7...1.25.8)

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements/azure_cosmos.txt

@@ -9,7 +9,7 @@ certifi==2019.11.28
 chardet==3.0.4
 idna==2.8
 six==1.13.0
-urllib3==1.25.7
+urllib3==1.25.8
 virtualenv==16.7.9
 virtualenv-clone==0.5.3